US3944931A - Multi-channel frequency converter having automatic control - Google Patents

Multi-channel frequency converter having automatic control Download PDF

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US3944931A
US3944931A US05/523,852 US52385274A US3944931A US 3944931 A US3944931 A US 3944931A US 52385274 A US52385274 A US 52385274A US 3944931 A US3944931 A US 3944931A
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output
frequency
signal
frequencies
delay
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Noboru Usami
Chuichi Sodeyama
Hirozi Shoyama
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Hitachi Ltd
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Hitachi Ltd
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03D—DEMODULATION OR TRANSFERENCE OF MODULATION FROM ONE CARRIER TO ANOTHER
    • H03D7/00—Transference of modulation from one carrier to another, e.g. frequency-changing
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03J—TUNING RESONANT CIRCUITS; SELECTING RESONANT CIRCUITS
    • H03J7/00—Automatic frequency control; Automatic scanning over a band of frequencies
    • H03J7/02—Automatic frequency control
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J7/00—Multiplex systems in which the amplitudes or durations of the signals in individual channels are characteristic of those channels
    • H04J7/02—Multiplex systems in which the amplitudes or durations of the signals in individual channels are characteristic of those channels in which the polarity of the amplitude is characteristic
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03D—DEMODULATION OR TRANSFERENCE OF MODULATION FROM ONE CARRIER TO ANOTHER
    • H03D2200/00—Indexing scheme relating to details of demodulation or transference of modulation from one carrier to another covered by H03D
    • H03D2200/0041—Functional aspects of demodulators
    • H03D2200/0094—Measures to address temperature induced variations of demodulation
    • H03D2200/0096—Measures to address temperature induced variations of demodulation by stabilising the temperature
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03D—DEMODULATION OR TRANSFERENCE OF MODULATION FROM ONE CARRIER TO ANOTHER
    • H03D3/00—Demodulation of angle-, frequency- or phase- modulated oscillations
    • H03D3/02—Demodulation of angle-, frequency- or phase- modulated oscillations by detecting phase difference between two signals obtained from input signal
    • H03D3/06—Demodulation of angle-, frequency- or phase- modulated oscillations by detecting phase difference between two signals obtained from input signal by combining signals additively or in product demodulators
    • H03D3/08—Demodulation of angle-, frequency- or phase- modulated oscillations by detecting phase difference between two signals obtained from input signal by combining signals additively or in product demodulators by means of diodes, e.g. Foster-Seeley discriminator
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03D—DEMODULATION OR TRANSFERENCE OF MODULATION FROM ONE CARRIER TO ANOTHER
    • H03D9/00—Demodulation or transference of modulation of modulated electromagnetic waves
    • H03D9/06—Transference of modulation using distributed inductance and capacitance

Definitions

  • the present invention relates to a receiver for receiving multi-channel broadcast and more particularly to a frequency converter which enables a VHF or UHF television receiver set to receive television broadcast waves using as their carriers superhigh frequency signals.
  • the frequency converter to enable the conventional TV receiver to receive the SHF broadcast comprises, for example, an antenna for catching the broadcast waves in the air, a local oscillator for generating at a time a single oscillation frequency, a mixer for mixing the signals induced in the antenna and the output of the local oscillator, and an amplifier for amplifying the output, that is, frequency-converted signal, from the mixer. If the antenna catches three kinds of broadcast waves having their respective carrier frequencies f 1 , f 2 and f 3 , the amplifier mentioned above will deliver the corresponding three kinds of signals having frequencies f' 1 , f' 2 and f' 3 .
  • the SHF signal can be effectively received by simply connecting the converter with the conventional television receiver set.
  • the frequencies f' 1 , f' 2 and f' 3 are so determined as to correspond to the channels to which no broadcast waves are alloted in the district in consideration.
  • the most important thing with such a frequency converter is the stability of the oscillation frequency of the local oscillator. The problem concerning the stability of the oscillation frequency will be described by the use of concrete numerical example.
  • the local oscillation frequency f l assumed to be set lower than the carrier frequency of the SHF channel, is such that
  • the video carrier frequency f 1 of the broadcast wave can be considered almost fixed since the broadcast station is always monitoring and correcting the fluctuation in the frequency, so that the fluctuation in the frequency f' 1 of the output of the converter depends mainly on the deviation of the local oscillation frequency f l , the variation + ⁇ f of the frequency f l causing the variation - ⁇ f of the frequency of the output of the converter.
  • the video carrier frequency of the broadcast signal induced in the antenna must be confined within a range of at least the predetermined value ⁇ 0.1 MHz. Accordingly, the local oscillator of the frequency converter must have a frequency stability as high as 0.1/11,306.75, i.e. about 1 ⁇ 10 - 5 .
  • a high frequency stability can be attained by (1) using an oscillator having a high frequency stability, such as quartz or crystal controlled oscillator and (2) automatically controlling the local oscillation frequency in such a manner that the detected deviation of the output frequency is always rendered to zero.
  • the first method cannot be employed in the television sets for domestic use since the associated device is very complicated and expensive. Moreover, in the present level of technique, even a quartz controlled oscillator having the highest frequency stability attainable will not be able to maintain the above said stability in the circumstances varying in ambient temperature, power source voltage etc.
  • the local oscillator of the frequency converter In order to automatically control the local oscillation frequency, it is necessary to design the local oscillator of the frequency converter so that it may generate in a change-over fashion different frequencies in accordance with the number of the broadcast waves, and to incorporate in the frequency converter mentioned above a frequency discriminator which detects the frequency of the output of the mixer or the output of the amplifier and whose output is fed to the local oscillator to automatically control the oscillation frequency.
  • the carrier frequency in the output of the mixer remains to be a fixed value f o for any channel received since the local oscillation frequency is changed over in accordance with the frequencies of the received signals. Accordingly, the channels to be received are selected by changing over the oscillation frequencies of the local oscillator and the channel selecting device or channel selector of the conventional TV receiver set to which the frequency-converted signals are applied, is adjusted to the frequency f o .
  • the frequency converter described above has the following drawbacks.
  • each of the plural TV broadcast channels will be separated from one another by about 12 MHz, as in the UHF band, the different frequencies generated by the local oscillator must differ from one another by about 12 MHz. As described before, however, the local frequency is to be around 11 GHz and it is technically very difficult to make a difference of 12 MHz with respect to such a high frequency.
  • 2.3 MHz the difference (4.5 MHz) between the video and the sound carrier frequencies.
  • the breadth of 2.3 MHz is about 20 times the value 0.1 MHz obtained above in the absence of frequency control.
  • the frequency stability in this case is 2 ⁇ 10 - 4 and this is a much relaxed condition in comparison with the previously obtained value of 1 ⁇ 10 - 5 .
  • the local oscillator In order to maintain the improved value under various conditions, however, the local oscillator must be provided with some auxiliary stabilizing means. Thus, under these circumstances, the local oscillator for generating not a single frequency but plural ones in change-over manner will add considerably to technical difficulties.
  • the conventional TV receiver sets are utilized in the reception system using such a frequency converter as enlarged upon above. Since the receiver set has a channel selector, the separate provision of a channel selecting function in the converter will cause an operative complexity and above all be uneconomical.
  • a first object of the present invention is to provide a frequency converter well adapted for the reception of the television broadcast in superhigh frequency band.
  • a second object of the present invention is to provide a frequency converter well adapted for the reception of the multi-channel television broadcast in superhigh frequency band.
  • a third object of the present invention is to provide a frequency converter which can be easily manipulated and is suitable for domestic use and well adapted for the reception of the superhigh frequency band television broadcast.
  • a fourth object of the present invention is to provide a frequency converter in which the frequency of the local oscillator can be securely and automatically controlled even in case where the converted signal contains a plurality of carrier signals having different frequencies.
  • the local oscillator generates at a time a single frequency and a specifically designed frequency discriminator is used as a circuit to detect frequencies for automatic frequency control, which discriminator delivers a zero output voltage for a plurality of predetermined frequencies and provides repeatedly frequency discriminating characteristics for the variation in the frequency.
  • the frequency discriminator is constituted by a means for delaying an input signal by a time ⁇ and shifting the phase of the input signal by ⁇ radians; a means for delaying an input signal by a time ⁇ /2 and shifting the phase of the signal by ⁇ /2 radians; a first adding means for adding an input signal to the signal having a delay time of ⁇ and a phase shift of ⁇ radians; a second adding means for adding the output of the first adding means to the signal having a delay time of ⁇ /2 and a phase shift of ⁇ /2 radians; a first subtracting means for making a difference between the output of the first adding means and a signal having a delay time of ⁇ /2 and a phase shift of ⁇ /2 radians; a means for rectifying the output of the second adding means; a means for rectifying the output of the first subtracting means; and a second subtracting means for making a difference between the outputs of the first and second rectifying means.
  • FIG. 1 is a system block diagram showing schematically one embodiment of the present invention.
  • FIGS. 2a to 2c are frequency spectra for the explanation of frequency converting operation.
  • FIG. 3 graphically shows the frequency characteristic of a frequency discriminator used in the present invention.
  • FIG. 4 is a block diagram of a first embodiment of a frequency discriminator utilized in the system block diagram of the present invention of FIG. 1.
  • FIGS. 5 to 7 show curves representing frequency vs. voltage characteristics for the explanation of the operation of the circuit shown in FIG. 4.
  • FIG. 8 is a block diagram of a second embodiment of a frequency discriminator utilized in the system block diagram of the present invention of FIG. 1.
  • FIGS. 1 and 2 show respectively the schematic block diagram of the present invention and the sketches of frequency spectra useful for the explanation of frequency converting operation.
  • the SHF television broadcast signal caught by an antenna 1 is fed to a mixer 2.
  • the TV signal has, for example, a frequency spectrum as shown in FIG. 2a.
  • Trapezoids 31, 32 and 33 indicate three broadcast channels used in a certain district, vertical line segments 34, 35 and 36 the associated video carriers, and vertical line segments 37, 38 and 39 the associated sound carriers.
  • the frequencies of the video carriers 34, 35 and 36 are designated respectively by f 1 , f 2 and f 3 . These frequencies are chosen to be within a band of, for example, 11.7 to 12.2 GHz.
  • the frequency band width f B occupied by each of the channels is determined to be, for example, 6 MHz while the channel interval f c of the respective channels is chosen to be 12 MHz.
  • the frequencies of the sound carriers 37, 38 and 39 are higher by 4.5 MHz than those of the video carriers f 1 , f 2 and f 3 , respectively. Namely, the system now in consideration is the same as the television broadcast system except that the video carriers are in superhigh frequency band. In the above description, it is assumed that the number of the broadcast channels is three, but it should be noted that the greater is the number, the more effective is the present invention.
  • each channel is independent of the others and all the channels may not be occupied, that is, some channels may be vacant of transmitted signal.
  • the channel 32 represented by dotted line in FIG. 2a means such a vacant channels.
  • the mixer 2 receives besides the SHF broadcast signals caught by the antenna a local oscillation signal (having a frequency f l ) generated by a local oscillator 3 and indicated by a vertical line segment 40 in FIG. 2b, and delivers an output having a frequency component that is the difference between the SHF broadcast signal frequency and the local oscillation frequency.
  • FIG. 2c shows the frequency spectrum of the output of the mixer 3.
  • trapezoids 41, 42 and 43 indicate the frequency-converted versions of the broadcast channels 31, 32 and 33, vertical line segments 44, 45, 46 the frequency-converted versions of the video carriers 34, 35 and 36, and vertical line segments 47, 48 and 49 the frequency-converted versions of the sound carriers 37, 38 and 39.
  • the frequency-converted video carriers 44, 45 and 46 respectively have frequencies f' 1 , f' 2 and f' 3 , which equal f 1 , f 2 and f 3 , minus the local oscillation frequency f l .
  • the channel breadth and the channel interval are maintained unaltered even after frequency conversion and respectively equal f B and f c .
  • the local oscillation frequency f l is so selected that f' 1 , f' 2 and f' 3 may coincide with the frequencies of the currently used video carriers in the UHF broadcast band.
  • the output of the mixer 2 is amplified by a wide-band amplifier 4 and the output of the amplifier 4 is fed to a conventional television receiver 6, which in turn selects a channel for reception of broadcast.
  • a part of the output of the amplifier 4 is applied also to the input terminal 101 of a frequency discriminator 10.
  • the frequency discriminator 10 delivers a zero output voltage at its output terminal 102 when the frequency of the signal applied to the input terminal 101 coincides with one of predetermined frequencies, but otherwise a positive or negative voltage at the output terminal 102 whose amplitude depends on the difference between the frequency of the signal applied to the terminal 101 and the predetermined frequency.
  • the frequencies predetermined in the frequency discriminator 10 have the same channel interval f c as shown in FIG.
  • the frequency discriminator 10 corresponds with the video carrier frequencies of the conventional VHF or UHF band broadcast waves.
  • the relationship between the input frequency and the output voltage, of the frequency discriminator 10 is represented by such a characteristic as shown in FIG. 3.
  • the predetermined frequencies for the frequency-converted video carriers are designated by f 11 , f 12 and f 13 , which are adjusted to coincide with the video carrier frequencies of the reception channels of the television receiver 6.
  • the frequency interval of these frequencies f 11 , f 12 and f 13 is set equal to the channel interval f c of the SHF broadcast signals.
  • FIG. 4 showing in block diagram a frequency discriminator as a first embodiment of the present invention.
  • To the input terminal 101 is applied the output of the wide-band amplifier 4 shown in FIG. 1.
  • the output branches off to an adder 12 and to a phase shifter 13.
  • the output of the phase shifter 13 is passed through a delay circuit 14 and then branches off to an amplifier 17 and to a delay circuit 15.
  • the output of the delay circuit 15 is fed via a phase shifter 16 to an amplifier 18.
  • the phase shifters 13 and 16 provide the same phase shift within the range of the frequencies of the signals processed.
  • the delay circuits 14 and 15 also have the same delay time.
  • the signal passed through the delay circuits 14 and 15 and the phase shifters 13 and 16 and amplified by the amplifier 18, is applied to the adder 12 and added there to the input signal applied directly to the adder 12.
  • the input signal at the terminal 101 is a simple sinusoidal wave represented by the formula:
  • the amplifier 18 delivers at its output terminal an output signal e 1 such that
  • the voltage applied to the first input terminal of the adder 12 is e o represented by the formula (1) so that the sum of e 1 and e o appears at the output of the adder 12.
  • the synthesized voltage be represented by e 2 , and e 2 is such that
  • the signal e 2 is given by the formula:
  • the amplitude of e 2 varies with the phase angle ( ⁇ + ⁇ ) including an angular frequency ⁇ , as shown in FIG. 5.
  • the output of the adder 12 is applied to both one of the input terminals of an adder 19 and one of the input terminals of a subtracter 20.
  • To the other input terminal of the adder 19 and the other input terminal of the subtracter 20 is applied the input signal which has been passed through the phase shifter 13 and the delay circuit 14 and amplified by an amplifier 17.
  • the voltages e 4 and e 5 are respectively applied via transformers 21 and 22 to rectifiers 23 and 24 so that dc voltages E 4 and E 5 corresponding to the e 4 and e 5 are developed across resistors 25 and 26.
  • the dc voltages E 4 and E 5 are given by the following formulas:
  • ⁇ E The variation of ⁇ E with respect to the phase angle ( ⁇ + ⁇ ) is as shown in FIG. 7.
  • the voltage ⁇ E varies sinusoidally with a period of 4 ⁇ .
  • the delay time ⁇ /2 of the delay circuit 14 or 15 is determined such that ##EQU1## where f c is the channel interval as described with FIG. 2. Since the channel interval f c is 12 MHz, the delay ⁇ /2 is about 83 nsec.
  • the formula (13) is therefore transformed into
  • the voltage ⁇ E varies sinusoidally with f, at a period equal to f c .
  • the frequency f 11 predetermined for the channel 41 in FIG. 2 in the frequency converter in FIG. 1 can be expressed by the use of f c , as follows.
  • the predetermined frequencies f 12 and f 13 for the other channels 42 and 43 can also be expressed as follows.
  • ⁇ E for the input frequency f 11 can be obtained by substituting f 11 in the formula (16) for f in the formula (15), the result being such that
  • phase shift ⁇ /2 of the phase shifters 13 and 16 is so determined as to satisfy the condition: ##EQU2## where m is zero or unity, then there is obtained a frequency discriminating characteristic in which ⁇ E vanishes for the input of f 11 and decreases with the increase in frequency in the neighborhood of f 11 .
  • ⁇ E provides a desired characteristic of frequency discrimination even for the frequencies f 12 and f 13 .
  • the characteristic of frequency discrimination as shown in FIG. 3 can be realized by the circuit as shown in FIG. 4.
  • phase shifters 13 and 16 described above have only to provide approximately equal phase shifts within the range of frequencies to be processed, i.e. a band of 36 MHz in case where the number of the broadcast channels is three and the frequency interval is 12 MHz, so that conventional phase shifters can be used to play the roles of the phase shifters 13 and 16. It is known from this that in case of a multiplicity of broadcast channels being used, the frequencies of the frequency-converted signals preferably belong to the UHF band.
  • the input signals to the frequency discriminator 10 is assumed to be a single sinusoidal wave, but in the actual reception of broadcast the signals of plural channels having different frequencies are applied to the discriminator 10, as shown in FIG. 2.
  • the part from the input terminal 101 to the transformer 22 is a so-called linear circuit, which responds independently to the signals having different frequencies.
  • the rectifiers 23 and 24 are nonlinear elements, the modulating actions among the plural signals take place in these elements.
  • an appropriate design of the constants in the rectifier circuit can sufficiently reduce the mutual modulating actions so that each signal may be regarded as rectified independently. Accordingly, the oscillation frequency of the local oscillator 3 can be automatically controlled to be a predetermined value, by feeding the output voltage of the frequency discriminator 10 back to the local oscillator 3.
  • the delay circuits 14 and 15 which are the important constituents of the frequency discriminator 10 can be used usually either ultrasonic delay elements using the time of the propagation of ultrasonic vibrations through medium such as glass or coaxial cables using the times of the propagation of electromagnetic waves therethrough.
  • the circuit structures can be simplified if an artifice to propagate the waves in both ways (i.e. in a reflective manner) through the medium, is employed.
  • FIG. 8 shows a control structure of a frequency discriminator as a second embodiment of the present invention.
  • only one delay circuit 27 is used in place of two. Namely, the signal applied to the input terminal of the delay circuit is reflected from the output end of the delay circuit to travel backward.
  • the delay circuit 27 is equivalent to the combined role of the delay circuits 14 and 15.
  • the terminal 27a is for the input signal to excite the delay circuit 27.
  • the input signal, after it has traveled a forward path in the delay circuit 27, is partially taken out through the output terminal 27b.
  • the terminal 27b plays the same role as the output terminal of the delay circuit 14 in the previous embodiment shown in FIG. 4 and it is from this terminal 27b that the output voltage corresponding to e 3 is derived.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Superheterodyne Receivers (AREA)
  • Channel Selection Circuits, Automatic Tuning Circuits (AREA)
  • Stabilization Of Oscillater, Synchronisation, Frequency Synthesizers (AREA)
  • Television Receiver Circuits (AREA)
US05/523,852 1973-11-17 1974-11-14 Multi-channel frequency converter having automatic control Expired - Lifetime US3944931A (en)

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Cited By (5)

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Publication number Priority date Publication date Assignee Title
US4567442A (en) * 1981-11-19 1986-01-28 Siemens Aktiengesellschaft Method and apparatus for demodulating time-discrete frequency-modulated signals
US20070297754A1 (en) * 2006-05-18 2007-12-27 Naoyuki Wada Receiving apparatus and method of controlling a receiving apparatus
US7734251B1 (en) 1981-11-03 2010-06-08 Personalized Media Communications, Llc Signal processing apparatus and methods
US7769344B1 (en) * 1981-11-03 2010-08-03 Personalized Media Communications, Llc Signal processing apparatus and methods
USRE47642E1 (en) 1981-11-03 2019-10-08 Personalized Media Communications LLC Signal processing apparatus and methods

Citations (2)

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Publication number Priority date Publication date Assignee Title
US3328700A (en) * 1964-11-04 1967-06-27 Magnavox Co Means for fine tuning television receivers with a.f.c. disabler
US3697885A (en) * 1970-12-04 1972-10-10 Rca Corp Automatic frequency control circuits

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3328700A (en) * 1964-11-04 1967-06-27 Magnavox Co Means for fine tuning television receivers with a.f.c. disabler
US3697885A (en) * 1970-12-04 1972-10-10 Rca Corp Automatic frequency control circuits

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Also Published As

Publication number Publication date
DE2454283A1 (de) 1975-05-22
DE2454283C3 (de) 1979-03-29
JPS531125B2 (enrdf_load_stackoverflow) 1978-01-14
JPS5081215A (enrdf_load_stackoverflow) 1975-07-01
DE2454283B2 (de) 1976-03-25

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